The novelist Hjalmar Söderberg may not be well-known in Britain but he is regarded as one of Sweden’s greatest writers. His short novel Doktor Glas, published in 1905, takes the form of a journal written over the course of a sultry summer. More than a hundred years on, it feels a presciently modern vision of the relationship between love, power and mortality.

Allan Edwall’s Sixties stage adaptation is somewhat unlikely West End fare — presented in Swedish with surtitles. It’s a one-man show, and the man in question is Krister Henriksson, a strikingly hangdog actor familiar to audiences here from the original Swedish TV version of Wallander.

Henriksson captures the Stockholm doctor’s wistful lyricism. At the same time he suggests his awkwardness, much of which has to do with women. Glas is both gruff and poetic, haunted and able to revel in the fact of his being so. He’s steeped in philosophy, quoting Schopenhauer casually, and keeps cyanide in his desk drawer, for purposes that are at first ambiguous.

When a young woman called Helga seeks his guidance, he responds with an expertise that’s as much moral as medical. Helga is apparently being tormented by her husband Gregorius. This older man is also Glas’s patient, and he’s a grotesque figure — a churchman who insists on what he thinks of as his physical “rights”. Glas decides to help Helga.

Henriksson is a lovely speaker and evokes Glas’s articulate manner with unflinching precision. He oscillates between jocularity and despair, sarcasm and resignation. As in Wallander, he’s a weary and isolated commentator on the rotten state of the world around him.

The production is Henriksson’s collaboration with director Peder Bjurman, and Bjurman provides a design that looks rather like an Edward Hopper painting.

The story and concept are absorbingly simple yet also clever in the way they blur the division between dreams and reality.

It’s fair to say that an extended piece of introspection isn’t an obvious candidate for theatrical interpretation. What’s more, Henriksson is obliged to sport an ugly microphone that juts past his right cheekbone. But this is an elegant, psychologically astute drama, and Henriksson is riveting.